Calling name and number information may be carried in SIP invites in the P-Asserted-Identity (PAI) header. To convey this info securely, SIP uses a transitive trust model, where adjacent network entities in the signaling chain trust the caller-ID info received from their previous-hop entity. The transitive trust model breaks down when there is an untrusted entity in the signaling chain. This can occur for SIP-PBX call scenarios where the untrusted SIP-PBX receives an incoming call from the service provider network and a feature (like call-forwarding) causes the SIP-PBX to redirect the call back to the service provider network. For example, in a transitive trust model, if Alice activates call-forwarding on her office phone to redirect incoming business calls to her mobile phone over lunch hour, the redirected SIP invite transmitted to the mobile phone may identify the SIP-PBX of Alice's office phone instead of the party attempting to call Alice due the untrustworthiness of the SIP-PBX.
The operation of such a transitive trust model may include, if Bob is the party attempting to call Alice, the service provider network sending a first invite to the SIP-PBX targeting Alice's office number. The first invite may contain SIP parameters identifying the calling name and number of Bob. When Alice has activated call-forwarding, the SIP-PBX may responsively initiate a second invite toward the service provider network targeting Alice's mobile number. If the service provider receiving the second invite determines the SIP-PBX to be untrusted, the service provider network may remove a received PAI header identifying Bob prior to transmitting a third invite to Alice's mobile phone. The PAI header identifying Bob may be replaced with a new PAI header identifying Alice's office calling name and number, which may be done in order to avoid calling name/number spoofing when the service provider network does not trust a calling name/number received from the SIP-PBX unless the name/number belongs to the SIP-PBX.
One non-limiting aspect of the present invention contemplates enabling the service provider to include caller-ID information for Bob when the SIP-PBX is untrusted in order to facilitate identifying Bob within the PAI header provided to Alice's mobile phone, which may be beneficial in allowing Alice to identify callers when forwarding phone calls from the untrusted SIP-PBX of her office phone.